The following article provides general information about sensor usage:

 

http://www.brainmaster.com/generalinfo/electrodeuse/electrodeuse.html

 

For demonstrations of basic sensor placement, see also on YouTube:

 http://www.youtube.com/watch?v=6xgVm6F2d2k

http://www.youtube.com/watch?v=Vu6UkHx6kz8